I. Field
The present disclosure relates generally to radio frequency devices, and more specifically to techniques for reducing the size and the power consumption of a radio frequency device.
II. Background
Radio-frequency based communication networks, such as voice and data transfer networks, are widely deployed in both wire and wireless environments, such as cell phones and cable set-top-boxes, to provide various services such as voice, video, packet data, messaging, broadcast, etc. These networks may be multiple-access networks capable of supporting multiple users by sharing the available network resources. Examples of such multiple-access networks in the wireless field for example include Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, and Single-Carrier FDMA (SC-FDMA) networks.
In radio-frequency based communication networks it is desirable to use radio-frequency transmitter integrated circuits that have single-ended radio-frequency outputs to achieve better efficiency in both area and number of components used. This reduces the number of pins and the number of external components. Multi-band and multi-mode solutions often use several transmitter paths so keeping single-ended RF outputs becomes of importance.
Currently, analog and/or radio-frequency integrated circuits, such as radio-frequency transmitter circuits, rely on differential (balanced) circuit architectures to accomplish better noise immunity, high carrier suppression and high isolation. A differential to single-ended conversion circuit is then often used between the differential input stage and the single-ended output stage. This differential to single-ended conversion for radio-frequency transmitter circuits is normally accomplished with the use of passive transformers which re-phase and the sum two differential signals. A shortcoming of the foregoing approach is that passive transformers are often large in area, require tuning to operate for different frequency bands, and in some cases more than one transformer is required for a complicated transmitter that has different signal paths. For example, the typical die area of such a transformer is about 600 um×600 um. A dual band solution could require two transformers requiring a total silicon area equal to 0.72 mm2. These transformers thus not only occupy relatively large silicon die area but also can couple magnetically to other sensitive circuits such as voltage controlled oscillators (VCO), low noise amplifiers (LNA)s etc. to cause interferences with these circuit, such as in the form of added noise.
Accordingly, there is a need in the art for radio-frequency based integrated circuits that have single-ended, radio-frequency outputs, but which achieve better efficiency in both area and number of components used, as well as current consumption.